Merge pull request #2087 into cross-win-osx.

Thanks to @offlinehacker for the fixes.

* 'crossdev' of github.com:offlinehacker/nixpkgs:
  gifsicle: add optional static builds, make gifview optional
  libjpeg_original: add optional static builds
  optipng: use system libpng & zlib, fix cross builds and add ...
  xcode: fix hash
  libarchive: *permanently* fix patch source and hash